New Scientist magazine reports that the US Air Force is spending shedloads of cash on an Active Denial System.

This is a high tech system which fires a tightly focused beam of microwaves that causes an intense, but theoretically harmless, burning sensation on the skin of its human targets. The ADS was developed by the Pentagon's Joint Non-Lethal Weapons Directorate. It has mounted a version on a truck and made a smaller version for infantry use.

The Air Force version, according to New Scientist, will be packed into a chopper and capable of handling multiple beams at once making it perfect for non-lethal crowd control. But apparently beancounters at the Government Accountability Office survey rated the ADS a big waste of money, and some researchers have questioned whether it really is harmless to its targets.

It is set to cost the Air Force $2 million to $10 million. However so far it has never been used, because there are concerns about its legality and its potential for unintentional harm. US laws actually forbid it from being used on US citizens.